1 Hall-Current Ion Sources - Wiley-VCH

1Hall-Current Ion Sources

1.1Introduction

Ion sources and the development of ion beams are produced by the creation of strongelectrostatic fields in plasma. For quite a long period of time, before the 1950s,electrical discharges were studiedwithoutmagnetic fields. It was believed that strongelectrostatic fields in a plasma volumewere impossible to develop. At that time, it wasexperimentally found that strong electric fields could be observed only in thin layersof Debye-layer scale near electrodes, in places where quasineutrality is broken.

Then, in the 1950s, successful experiments confirmed the theoretical possibilityof magnetic field utilization providing magnetization of electrons, which sharplyhelped to increase plasma electrical resistance and to obtain large electric fields withthe development of Hall currents in crossed electric and magnetic fields in a plasmavolume.

TheHall-current ion source operation is based on the physical principles of electronmagnetization and on the increase of plasma resistance and electron lifetime, duringwhich electrons can interact with neutral particles and ionize them. This concept wasimplemented in the development of modern electric propulsion devices for spaceapparatuses, which were later transformed and are now used as ion sources.

In the ion source discharge channel, the electrons aremagnetized, ifvet� 1 (ve isthe electron cyclotron frequency in a magnetic field; t is the average time betweenelectron collisions with other particles and the discharge channel walls). The ions areusually notmagnetized,vit� 1 (vi is the ion cyclotron frequency in amagneticfield;t is the average time between ion collisions with other particles and dischargechannel walls) andmove under the applied electrical field between the anode and thecathode. During discharge in the magnetic field, electrons move to the anode not instraight lines, but rather in circles in crossed magnetic and electric fields; theyexperience collisions with working gasmolecules, ions, discharge channel walls, andalso due to oscillations. Ions are not influenced by themagnetic field, but move fromtheir places of origin, usually near to the anode into the cathode direction along theelectricfield.Moving from the ion source, an ionflow captures the necessary numberof electrons for neutralization and develops what is called an ion beam, though the

Industrial Ion Sources: Broadbeam Gridless Ion Source Technology, First Edition. Viacheslav V. Zhurin.� 2012 Wiley-VCH Verlag GmbH & Co. KGaA. Published 2012 by Wiley-VCH Verlag GmbH & Co. KGaA.

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ions are accompanied, in general, by electrons. Electrons drifting in the azimuthdirection neutralize the space charge of ions in the discharge channel. Due to thisphysical fact, inHall-current ion sources (contrary to gridded ion sources) there is nolimit for an ion beam current that exists in gridded ion sources caused by a spacecharge of ions. Because electrons move in circles in crossed magnetic and electricfields, the ion sources and thrusters use a principle known as ion source-thrusterswith closed electron drift.

Part of the regular operation ofHall-current ion sources is the existence of a varietyof oscillations of discharge current and voltage in a certain range of values, especiallyat low and high values. Operatingmagnetic fields depend on ion source dimensions,but as a rule, magnetic fields in a discharge channel of the cylindrical ion sources arenot very high: from about 100 G to a maximum of 500 G. It is necessary to note thatlinear ion sources with closed electron drift, which will also be discussed in the book,can have substantially higher magnetic fields, sometimes over 1000 G.

In the following sections, existing gridless ion sources and their designing featuresand differences will be described, followed by a discussion of the main physicalcharacteristics of such ion sources.

1.2Closed Drift Ion Sources

Closed drift ion sources (CDIS) were developed to a very high degree of efficiency asthrusters in the 1960s; then in 1972, Russian scientists launched a �Meteor� satellitewith the thruster based on the closed electron drift principle.

Currently, every third Russian satellite is equipped with a closed electron driftthruster. There are already over 200 thrusters in space; many CDIS are on Americansatellites too.

Besides the magnetization of electrons, one of the basic ideas in the successfuloperation of CDIS for a broad range of discharge voltages, currents, and a variety ofgases is that themagnetic field in a discharge channel increases from the anode to anion source exit. In otherwords,CDIS is an ion source with a positivemagnetic gradient ina discharge channel. The main �operating� magnetic field is a radial component. Thedischarge channel has an annular form.

In general, there are two types of CDIS: magnetic layer ion source (MLIS)(Figure 1.1) and two modifications of anode layer ion source (ALIS), shown inFigure 1.2a and b [1, 2] as schematics and three-dimensional pictures. Themain partsof CDIS – anode, magnetic poles, andmagnetic coils developing themagnetic field –are shown in these figures. Cathode neutralizers are not shown.

In Figure 1.2a and b, ALIS have a different placement of anode: in Figure 1.2a, it isinside the discharge channel; and in Figure 1.2b, some of the anode�s surface isextended outside the magnetic poles.

Such an extended anode provides a slightly narrower range of operationaldischarge voltages, but it has the advantage of sharply reducing the erosion ofmagnetic poles in comparison with regular ALIS anode placement (Figure 1.2a.)

2j 1 Hall-Current Ion Sources

The dimensions of a cylindrical form CDIS are from about 20mm of the exit-plane diameter up to 290mm (recent thruster design). As ion sources, CDIS areused from about 50 to 100mm of exit diameter. Working gases are Ar, Xe, O2, N2,H2, CH4, and others.

The range of operation for discharge voltages is Vd � 80–1000 V; for dischargecurrents, it is Id � 0.1–15 A. The mean ion beam energies are about Ei � 0.7 eVd

(in eV); the ion beam current is about Ii� (0.7–0.8) Id. The erosion rate of the anodeis negligible; the erosion rate of magnetic poles is substantial, though for ALIS, theerosion rate of poles with an extended anode area outside the discharge channel [2]is negligible. The ion beam divergence for MLIS is about 20� (for 70–80%) of ionbeam flow; for ALIS, it is about 15–20� [1]. The hollow cathode (HC) is utilized as asource of electrons for ion beamneutralization and ionization of neutral atoms;HCerosion is negligible.

In thin film technology, cylindrical CDIS are not widely utilized. However,Diamonex [3, 4] use cylindrical MLIS for DLC coating. Russian companies, Platarand MIREA use cylindrical MLIS for a variety of thin film tasks (etching, sputtering,ion beam assistance). ALIS modification without an external source of electrons isutilized extensively by many companies, mainly in the form of linear ion sources ofdifferent dimensions (up to 300 cm long).

CDIS advantages:

1) High transformation of a discharge current Id into an ion beam current Ii, Ii/Id�0.7–0.8, with utilization of an external source of electrons and with adequatemagnetic field optimization.

Figure 1.1 Magnetic layer closed drift ion source.

1.2 Closed Drift Ion Sources j3

2) Wide range of discharge voltages (ion beam mean energies), from aboutVd � 80–1000V, Ei¼ 55–700 eV.

3) Optimummagneticfields for cylindrical CDIS are in the range of 100Gto 600G;for linear ALIS, themagnetic fields are usually substantially higher, over 1000G.

4) Because of good magnetic field optimization, the cylindrical CDIS can operateup to about 1.5 kWof applied powerwithout awater-cooled anode.Hot discharge

Figure 1.2 (a) Regular anode layer closed drift ion source. (b) Anode layer closed drift ion sourcewith extended anode to reduce sputtering of magnetic poles.


plasma with an optimized magnetic field is well separated from the dischargechannel walls and anode.

Shortcomings:

1) Need for a variety of operating conditions in magnetic field optimization. Theratio of the ion beam current to the discharge current Ii/Id¼ f(Hmax) is not alinear function of themagnetic field, and themaximumdepends on the workinggas, discharge voltage, and current. Optimization is provided by magnetic coilswith variablemagnetic fields. Permanentmagnets can only be used for a specificselected range ofVd and Id and aworking gas. In practice, notmany userswant toperform such optimization.

2) Operation of CDIS without an external source of electrons in the so-called self-sustained discharge [5] (discussed in subsequent chapters) produces low trans-formationof the discharge current into an ionbeamcurrent Ii� (0.05–0.1) Id andhigh spread of ion beam mean energies Ei � (0.4–0.5) eVd (eV); and in theion beam energy distribution, there are ions with low (from several eV) and high(up to twice eVd) distribution. The length of ALIS is usually in the range 15–20 to100, 200, and even 300 cm.

1.3End-Hall Ion Sources

The discharge channel has a cylindrical form with a massive hollow conical anode.The cathode, serving as a source of electrons, is usually in the form of a hot filament(HF) or HC. Generally, electrons are only magnetized at the exit part, where themagnetic field has a radial component connecting to the externalmagnetic pole. Alsoat the exit, themagnetic field is quite low because the end-Hall ion source utilizes thepermanentmagnet�smagneticfield, which decreases from the place under the anodewhere a gas distributing system is usually located. The magnetic-field value on thepermanent magnet top (or on electromagnet) is about 1–2 kG; at the ion source exit(front flange), this magnetic field is reduced to about 50–100 G. Due to this, the end-Hall ion source can be considered as a source with a negative gradient of magnetic field.The next series of figures show a variety of end-Hall-type ion sources with the

following main parts labeled: anode, insulators, body (magnetic path), reflector-gasdistributor, working gas, permanent magnet, magnetic coil, magnetically soft iron,and conical insert. The cathode is not shown; it is either HF or HC. (Cathodes arediscussed later in Chapter 5.)Information about one of the first end-Hall-type ion sources was published in

1973 [6]. Figure 1.3 presents a schematic drawing and three-dimensional picture oftheHall-current ion source for the development of low-energy ions, indicating an exitarea for the neutralized ion beam; a front flange; a discharge channel made ofdielectricmaterial; an anode connected to a power supply (not shown); a backflange; acathode as an HF; a working gas; and a system of electromagnetic coils providing anon-uniform axial symmetric magnetic field distribution in a discharge channel.Amagnetic field in the discharge channel is sufficient formagnetization of electrons

1.3 End-Hall Ion Sources j5

(vete � 1). At the same time, ions are not magnetized (viti < 1) in the same way asclosed drift ion sources-thrusters. The ion source was operated in stable conditionswith several working gases, such as hydrogen (H2), nitrogen (N2) and argon (Ar), atdischarge voltagesVd¼ 150–600Vandwith discharge currents Id¼ 0.15–1.0 A. Also,it was reported that the ion beamangular divergencewas 16� and the ion beamenergywas close to the discharge voltage in eV.

The distinctive feature of this ion source is the presence of the cathode neutralizerinside the discharge channel. In all further designs, the cathode neutralizer is outsidethe discharge channel. The front flange, which has a small conical opening, doesnot allow the extraction of high ion beam currents. With the discharge currentsId¼ 0.15–1.0 A, the ion beam currents were Ii¼ 0.4–30mA. In other words, thedischarge current conversion into the ion beam was quite low.

The main design of an end-Hall ion source, which is still used by most producers,is presented in Figure 1.4. As shown, a hollow cone-shaped anode and a magnetic

Figure 1.3 One of the first Hall-current low-energy ion sources [5]. HF cathode is in the dischargechannel.

Figure 1.4 End-Hall ion source with permanent magnet on axis [7].


fieldmade by one or several permanentmagnets are placed on the source�s axis underthe reflector. The permanent magnet is usually fabricated from Alnico, either 5 or 8;Alnico magnets are good for sustaining high temperatures up to about 540 �C. Thisdesignwas suggested inEnd-Hall IonSource, byH.R.Kaufman andR.S.Robinson [7].It was developed and extensively studied at Kaufman & Robinson Inc. (K&R), with atleast three different dimensions (Mark I, Mark II, Mark III) and discharge currentsfrom under 1 A up to about 15 A and discharge voltages from about 50V up to 300Vwith various working gases. After its patenting in 1989, it was produced byCommonwealth Scientific Corporation (CSC) for about 10 years, and later in1999 by Consolidated Vacuum Corporation (CVC) and in early 2000 by VeecoInstruments. It is necessary to note that Veeco and K&R continue to provideimprovements to this design, which will be discussed later. The main design createsa simple and reliable device. Many foreign ion source producers, especially Chineseand S. Korean companies, made similar designs.

This and other varieties of end-Hall ion sources are characterized by the followingfeatures:

1) Overall dimension of the outer flange for the exit of an ion beam. Depending onthe geometry and outerflange, end-Halls are designed for application of a certainworking gasmassflow,which translates into a discharge current and then into anion beam current. The external flange, as a rule, is made of a soft magnetic ironand is part of a magnetic circuit–magnetic pole; the external shell of the ionsource is also fabricated of a soft iron.

2) Geometrical dimension of the anode, which is usually several centimeters inlength and diameter. Anodes can bemade of a variety ofmaterials that determinethe electrical conductivity, its participation in a thin film process (as a contam-inant, or chemical element that can be a part of a thin film), and in some cases,possible resistance to anode �poisoning.� Anode �poisoning� is usually adeposition of thin films of reactive gas compositions with the anode, dischargechannel, and vacuumchambermaterials. These dielectric depositions drasticallychange the operational characteristics of the ion source, decreasing majorparameters such as the ion beam current, and mean energy. This unpleasantfeature will be discussed in detail in Chapter 6.

3) Design of a working gas introduction into a gas discharge channel, in particular,how aworking gas is applied; how the area under the anode is designed; howwellmixed aworking gas is when applied into the anode area; if anyworking gas has apossibility to escape from a discharge channel before being ionized by an appliedelectric potential; how the electrical conductive plate (sometimes called as areflector) between the anode area and magnet–magnetic pole (where a workinggas usually is applied) is affected by an ion beam that (in many cases of end-Hallion sources) has a component directed into the side of a reflector causingsputtering, producing damage, and contaminating an ion beam with thereflector material.

4) Magnetic field value in a discharge channel and how magnetic field lines aredirected; is a magnetic field gradient positive (in certain cases, an end-Hall ion


source can be designed with a positive magnetic field gradient) or negative; howpermanent magnets or magnetic coils are placed; what kind of material per-manent magnets are made of because it is important not to apply high levels ofheat to magnets due to the possible threat of being demagnetized.

5) In almost all plasmadynamic systems in which discharge takes place in electricand magnetic fields, and especially in the presence of crossed electric andmagnetic fields, there are various types of oscillations and instabilities of maindischarge values: discharge current and voltage. The analysis of plasma para-meters in ion sources shows that the ion beam energy spread is determined bythe extended region of ionization and oscillations of electrical potential in adischarge channel. Development of ions with energy exceeding eVd shows thatoscillations play an important role and produce a significant impact on the ionbeam current and the energy of ions. Detailed description of various types ofoscillations and instabilities will be presented in Chapter 3.

Figure 1.5 shows the samedesign as Figure 1.4, where amagnetic coil [7] is utilizedinstead of a permanent magnet. A magnetic coil requires a separate power supply,but it allows changing magnetic field values in the discharge channel over abroader range. For those who want to use a magnetic coil, it is necessary to notethat the magnetic field distributions provided by a permanent magnet and amagnetic coil are slightly different, and the discharge behavior is slightly differentas well. Only scrupulous investigations show a different behavior of ion beamparameters.

Figure 1.6 shows an end-Hall of the S. Korean company, VTC-Korea [8]. Inthis design, a soft iron cylinder is inserted to continue amagnetic path close to a gasdistributor reflector in order to reduce the high-temperature impact on a perma-nent magnet.

The reason for inserting such a soft iron cylinder is the fact that manyproducers are trying not to use Alnico permanent magnets because they canget much higher magnetic field values with, for example, Nd-Fe-B magnets.

Figure 1.5 End-Hall ion source with magnetic coil on axis [7].


However, Nd-Fe-B magnets are significantly more sensitive to high temperaturesand their maximum operational temperature is about 150–200 �C, depending onthe magnet�s quality.

As shown in Figure 1.7,magnets are placed at the base of an ion source body [9]; asoft iron cylinder is placed where the permanent magnet is usually located on theion source axis, similar to Figure 1.4. This company [9] also utilizes regularplacement of a permanent magnet at the ion source base. This end-Hall ion sourcedesign is also equipped with a water-cooled anode and water-cooled magnetassembly.

Utilization of a soft-iron cylinder has another advantage: if an ion beam wouldpenetrate a reflector (and this happens quite frequently), it would not harm amagnet.

Figure 1.6 End-Hall with soft iron on top of permanent magnet to reduce temperature impact onmagnet [8].

Figure 1.7 End-Hall with magnets at base; soft iron is used instead of magnet; design reducestemperature impact on magnets [9].


As shown in Figure 1.8, the gas distribution area is substantially increased.Working gas is applied through holes that have a certain angle to provide a gasvortexflow for betterworking gas distribution [10]. This distribution increases the ionbeam current in comparison with the regular end-Hall design (Figure 1.4), whichtranslates to improved conditions for working gas ionization and, correspondingly,to a higher ion beam current than in a regular end-Hall.

Figure 1.9 shows another version of a gas distribution area with a straight-through working gas flow. According to Svirin and Stogny [11], in this design thegas distribution is arranged by the conical inserts and the hole. Here, theelectromagnet is utilized for finding the optimummagnetic field, and it is claimedthat such a design provides a higher ion beam current than in the regular end-Hall(Figure 1.4).

Figure 1.8 End-Hall with buffer area for improved gas distribution [10].

Figure 1.9 End-Hall with hollow insert under anode reduces insert�s sputtering [11].


Figure 1.10 shows an end-Hall ion source with a discharge channel that is underthe anode potential, including a gas distributing area-reflector [12]. Our experimentswith a similar design showed the following features of such a design:

1) Reflector connected to the anode operates as the anode itself. An electron currentdelivered by an external source of electrons (neutralizer) becomes attracted tothe central part of a reflector; mainly a longitudinal magnetic field providesconfinement of a discharge area and directs straight to the center of a reflectoranode.

2) Such a design reduces the ion beam current compared to a reflector, which isunder a floating potential. For example, for argon working gas, a dischargevoltage Vd¼ 50V and discharge current Id¼ 5 A, and an ion beam current forend-Hall with a floating potential Ii¼ 0.8 A; for the end-Hall ion source with areflector connected with anode, this value Ii¼ 0.4 A. For Vd¼ 100V, Id¼ 5 A, anion beam current for a floating potential design Ii� 1.2 A and for a reflectorconnected with an anode Ii� 0.6 A.

In many cases, producers of end-Hall ion sources make the anode and reflectorfrom various materials, but mainly of stainless steel.

Here are some considerations about the utilization of the reflector and anodemade of stainless steel. The application of high currents and voltages leads to thestainless sputtering and development of magnetized flakes adjusted to a reflectorand standing on its top. Some flakes are several millimeters in length and cancreate an electrical connection between a reflector and an anode. In this case and asnoted above, an ion beam current will be reduced substantially. A reflector will bedamaged faster and an ion beam will be �dirtier� (more sputtering erosion of areflector area). To avoid such a situation, it is necessary to frequently inspect an ionsource discharge channel, and the reflector and anode must be cleaned regularly.Utilization of other materials, like Ta, Ti, Hf, and Mo, can be a good substitution

Figure 1.10 End-Hall with connected anode and reflector; working gas distributed through a�shower cap� [12].


for stainless steel. They are sputtered less and their components can participate incertain depositions of these materials.

Figure 1.11 shows an end-Hall design with the indirect water-cooled anodethrough a dielectric plate [13]. In order to have high ion discharge currents andvoltages (higher ion beam currents and energies) with high electric powers releasedinto a discharge channel, and not to overheat the main part of a discharge channelanode, it is necessary to water cool the anode because end-Hall-type ion sources havea low efficiency of transformation of the discharge current into the ion beam current.Water-cooled anode designs have been practically developed from the beginning ofthe end-Hall ion source introduction. In general, it is a water flow in the anode thathas a cavity with electrical separation of the anode potential through the insulators.The insulators must be clean, and the water should have no contaminating particles.That is why purifiedwater is sometimes utilized, and from time to time the insulatorsmust be cleaned of any contaminating residue.

Water-cooled anodesmake it possible to apply at least twice asmuch electric powercompared to radiation-cooled anodes.

Figure 1.11 [13] shows a schematic design of an unconventional anode-coolingsystemwhere the anode is cooled through a dielectric plate.Waterflows in a cavity of acopper plate under a dielectric plate. The anode, in such a case, is not directly cooled,but through the dielectric plate and at high applied electric powers of about 3 kW(Vd¼ 200V, Id¼ 15 A), it can be heated to very high temperatures of about 1070 �C.With the direct water-cooled anode, it is heated to 500 �C; at the same time, the gasdistributor reflector has decreased its temperature from 1050 �C (direct watercooling) to 630 �C. In a vacuum of about 10�5 – 10�3 Torr, the mean free path ofparticles is substantially longer than the dimensions of an ion source and there is noconvectional heat transfer. In the points of connection of any solidmaterial, there arevery limited areas of a contact. In such a case, the main heat transfer is realized byradiation only.

Figure 1.11 End-Hall with water-cooled anode through a dielectric plate; such design helps fastassembly [13].


However, such a design has certain advantages in comparison with the directwater-cooled anode:

1) Because the anode is not connected with a water flow, the whole design is verysimple. The discharge channel and anode can be assembled–disassembled in afew minutes if the source is cooled off.

2) In the problem of so-called anode �poisoning� [14] (discussed in Chapter 7), theradiation-cooled anodes and the anode design (Figure 1.11) in some dielectricand insulating depositions do not stick like a water-cooled anode surface due tothe high heated anode surface. Such end-Hall ion sources can operate longer inconditions of anode bombardment by dielectric and insulating particles.

However, the anode surface with indirect coolingmust be carefullymonitored andnot exposed to temperatures at which the anode surface couldmelt. Also, a sputteringeffect that continuously takes place by electrons increases with a surface�stemperature.

This design showed slightly better performance than a regular end-Hall designwith the discharge current transformation into the ion beam current with Ii� 0.3 Id.

Figure 1.12 presents an end-Hall ion sourcewith not only awater-cooled anode, butwith water-cooled magnets. For certain technological processes that are highlysensitive to change of temperature regimes in the discharge channel, such a designserves very well. A soft iron cylinder completely substituted a permanent magnetwith a series of smaller dimension magnets placed at the lower flange base. As aresult, such a design can operate at a high applied electric powers of about 3 kW.Also, this design showed a very low sputtering rate of the gas distributor reflector.

Figure 1.13 presents the unconventional gas application into the discharge channelwith a regular type end-Hall ion source, similar to that shown in Figure 1.4. It did not

Figure 1.12 End-Hall with water-cooled anode and magnets helping stabilizing operatingparameters [15].


show any advantage in the discharge current transformation; it gave Ii� 0.2 Id.However, a sputtering erosion of the reflector is substantially lower than for a regulargas application (Figure 1.4).

Figure 1.14 shows a working gas application through the anode. Despite thecomplexity, this gas introduction has certain advantages, such as improved ion beamenergy distribution, which is substantially narrower than with a regular gas appli-cation (Figure 1.4). A protective cap placed on a permanent magnet gives a signalwhen an ion beam goes through the reflector [10]. Also, in such a case, the gasdistributor reflector experiences significantly less sputtering – about half as muchas the regular one.

Figure 1.13 End-Hall with working gas applied from top, between anode and upper flange; lowreflector�s sputtering.

Figure 1.14 End-Hall with working gas through anode; protective cap over a magnet gives signalwhen ion beam goes through reflector [10].


Figure 1.15 [16] shows a special end-Hall design with a grooved anode andplacement of the baffle in the presence of reactive gases that �poison� the anode,or at least substantially increase the operating time of the anode. The grooveshave sides that do not receive depositions of dielectric or insulating particles.These sides are in the shadow groove parts because in the ion source pressureoperating conditions with the long mean free path of particles, the particlespropagate along straight lines from their points of origin without collisions withother particles. Thus, a certain part of the anode remains without depositionfrom contaminating particles returning back into the ion source dischargechannel from a target-substrate or vacuum chamber parts. These parts withoutdepositions gradually become deposited, but it can take tens, even hundreds ofhours. The non-deposited parts of the grooved anode operate for quite a longtime with nominal parameters.

In this work, a metal baffle placed between the anode and the front flange was alsoutilized. The baffle serves as a shadow for the anode�s parts. In this case, the anodeoperates with reactive gases even longer than with the grooved anode, even thoughthe ion beam current is reduced by a factor of about 0.25 in comparison with thenominal. For processes with ion beam currents that are not high, the increase in thedischarge current with the additional baffle can be very helpful in working withreactive gases for longer periods of time without cleaning the ion source anode.

For a period of time, the end-Hall design was investigated as a thruster for electricpropulsion technology. Detailed tests of the end-Hall design as a thruster revealed alow thrust efficiency compared with the closed electron drift thrusters, and it was notseriously considered as an electric propulsion device. The problem is that the end-Hall ion source thruster has a negative magnetic field gradient in the dischargechannel, and this leads to the development of various oscillations of dischargeparameters and low ionization transformation of a working gas [17]. However, due tothe simplicity of the concept, several hybrid designswere developedwith the end-Halland closed drift properties for use as a thruster (Figure 1.16) [18] and an ion source(Figure 1.17) [19].

Figure 1.15 End-Hall with grooved anode and baffle to reduce anode �poisoning� [16].


Figure 1.16 shows a hybrid ion source-thruster suggested in Cylindrical GeometryHall Thruster byRaitses andFisch [18]. As one can see, this device is similar to a closedelectron drift thruster in which the central internal magnetic pole is substantiallyshorter. The magnetic-field gradient is provided by two electromagnetic coils. Thethruster showed quite good efficiency, though it is still less than a regular closedelectron drift thruster.

Figure 1.17 shows the schematic design of a similar hybrid ion source; in this case,a permanent magnet is utilized [19]. A soft-iron cylinder is placed in front of themagnet to reduce possible thermal stress on the magnet at highly applied electricpowers. The positive magnetic field gradient is provided by two magnetic shunts.Similar to a regular closed drift thruster, this design is quite sensitive to the rate of amagnetic field gradient and to the ratio of the magnetic shunt lengths, which areimportant as the additional coefficient influencing the operating parameters. Italso has a good discharge current into an ion beam current transformation rate,Ii/Id� 0.7–0.8. This design still needs further detailed experimental work.

Figure 1.18 shows the end-Hall ion source with a magnetron HC discharge [20].This recently developed ion source is based on the concept of a closed drift thruster

Figure 1.16 Hybrid end-Hall and closed drift ion source-thruster with electromagnets formagneticfield [18].

Figure 1.17 Hybrid end-Hall and Closed Drift ion source-thruster with permanent magnet softiron and shunts for positive magnetic field gradient [19].


with the anode layer. Itmainly consists of anannular anodeanda cylindricalHCenclosedby magnetic poles and an inner shield. The magnetic field in the discharge channel isproduced by a SmCo permanent magnet on Fig. 1.18 it is shown with a magnetic coil,back shunt, and inner and outermagnetic poles. Acylindricalmagnetic ring is shortenedand centrally inserted as an inner magnetic pole. The cylindrical magnetic permeabilitytube strengthens themagnetic field close to the annular anode in the discharge channel.Theworkinggas is introduced into theHCregion via an inlet in the gasdistributor. Thereis no external emissive element utilized with this ion source.

Here are some considerations about this design. This ion source dischargeoperates in a self-sustained modification at the discharge voltages (discussed inChapter 4) from Vd¼ 300 V and up to 450 V, with the discharge currents fromId¼ 1 Aup to 4 A. Because it operates with discharge in a self-sustained regime, noexternal source of electrons is utilized. Instead, the external magnetic pole andinternal magnetic pole are utilized as cold cathodes to produce secondary electronsfor ion beam neutralization. This ion source is typical of the ALIS (Figure 1.2a)utilized bymany companies for cleaning and sputtering without an external sourceof electrons, with a broad ion beam energy distribution, a low ion beam current,and a low mean ion beam energy value ratio to a discharge voltage. This ion sourcewas referred to as end-Hall by the authors, but we would classify it as a hybridbetween a closed drift and end-Hall ion source. For certain technological tasks(cleaning, sputtering), this ion source can be a very suitable device. It needs to bequalified with various working gases, and cold cathode sputtering rates should bemeasured to estimate an ion beam purity.

Also, it needs to be checked for the proper ion beam neutralization, with targetsplaced at different distances from the ion source.

Figure 1.19 shows an end-Hall ion source design with the gas distributor reflectorhaving additional material on the reflector�s top. The additional piece of materialincreases the reflector�s thickness and its lifetime, which was previously reduced byan ion beam sputtering (discussed above). This reflector can bemade sectional, withthe central partmade of a specificmaterial that can be part of the thin film deposition

Figure 1.18 Hybrid end-Hall with anode layer ion source without external source of electrons [20].


process (for example, with the tantalum, or titaniummaterial during obtaining theseelements oxides, etc.).

Also in this design, the exit flange-external pole ismade of sections. The lower partis separated by a dielectric piece, and the lower flange part is under a floatingpotential. The electric potential induced during an ion source operation by reflectingwith its potential (usually of about 0.5Vd) helps in reducing the ion beam divergence.

Figure 1.20 shows a new design of an end-Hall ion source with a two-chamberanode and aworking gas introduced through the anode [21]. Such a design provides avery uniform working gas distribution and has proved to be more efficient thanregular designs. Working gas introduction in the anode area accomplishes theionization process in a shorter distance at the anode by applying electric potentialonly in a narrow region, leading to a high ratio of the mean ion beam energy to thedischarge voltage times electron charge. In regular end-Hall ion sources, Ei/eVd �0.6–0.7. In this new end-Hall design with a two-chamber working gas introduction,this ratio Ei/eVd � 0.9. This design will be discussed in detail in Chapters 5 and 9.

Figure 1.19 End-Hall with improved features: reflector with �hat�; floating potential flange toreduce ion beam spread.

Figure 1.20 End-Hall with double-chamber anode and working gas through anode to improve ionbeam energy distribution [21].


1.4Electric Discharge and Ion Beam Volt–Ampere Characteristics

Electric discharge in a gas is the method of obtaining ions in an ion source. In over100 years of electrical discharge studies, and especially in devices designed forobtaining controlled flows of ions and electrons, it was found that in the particularrange of pressures of 10�5 – (1–2)� 10�3 Torr of working gases when an ion beamsatisfies the conditions for thin film technology, electric discharge exists in variousmodifications.

There are twomain regimes of discharge in the ion sources: (1) a nonself-sustainedregime and (2) a self-sustained regime. A nonself-sustained regime requires acathode emitting electrons for discharge ignition and its maintenance. A self-sustained regime does not need an external source of electrons. After ignition, aself-sustained discharge maintains its existence by a sufficient electric potential(Vd¼ 300–350V and above) applied between the anode and any conductors in adischarge channel (walls, flange) that can serve as cathodes with ions and electroncollisions with such conductors (high potentials, in principle, can generate electronswith dielectric and insulators surfaces, but with less probability than withconductors).

This discharge produces a sufficient number of secondary electrons from ionbombardment of the discharge channel and parts.

The characteristics of a self-sustained discharge ignition and its extinction dependon several factors: (1) pressure condition in a discharge channel; (2) gas type,especially its ionization potential; (3) means of gas introduction into a dischargechannel: uniformity, throughoneor a series of holes, slits,mixing; (4) geometry of theanode and its relative placement cathode serving parts; and (5) magnetic field valueand its distribution.

In order to discuss a nonself-sustained discharge and its role in Hall-current ionsources, it is best to start with the analysis of theVolt–Ampere (V–A) characteristics ofdischarge in theHall-current ion sources, although in general, V–Acharacteristics forboth types of ion sources (CDIS and end-Hall) demonstrate a similar behavior.

In Figure 1.21, the upper curve 1 shows typical V–A characteristics of high currentintense discharge of an end-Hall type ion source for discharge current Id¼ 5 A as afunction of discharge voltage, Id¼ f(Vd); a discharge current constancy is regulated byaworking gasmassflow that is substantially changing fromhigh to lowwhilemovingwith discharge voltages from low to high values. The working gas is argon, and thepressure in the vacuum chamber is between 5� 10�5 and (1–2)� 10�3 Torr. Thelower curve 2 presents an ion beam current Ii as a function of discharge voltage, Ii¼f(Vd). The discharge between the anode and the cathode is maintained by electronemission provided by a cathode placed outside of the ion source.

The source of electrons is either HF or HC. For the conditions in the end-Hall ionsource, a magnetic field of a permanent magnet or electromagnet is, in general,between about 500 and 1300G (depending on ion source dimensions), which has amaximum value at the top of a gas distributor-reflector. This means that a magnetic-field value is 300–500Ghigher on amagnet�s top [It is agreed bymost producers that

1.4 Electric Discharge and Ion Beam Volt–Ampere Characteristics j19

the top of a permanent magnet looking to a gas distributor will be a North pole.], or1000–1800G. Variations in low and high values are acceptable, depending on aparticular ion source task. For comparison, in a closed electron drift ion source, amagnetic field of a permanent magnet or electromagnet is between 100 and 500G ofthe maximum value, which is usually at the exit flange (depending on working gasand ion source dimensions).

High current electrical discharge inHall-current ion sources (Figure 1.21) consistsof two types: a nonself-sustained and a self-sustained discharge [22]. A nonself-sustaineddischarge takes place for discharge voltages from about Vd� 50–60V for an end-Halloperating with argon working gas and other noble gases; from about Vd � 80–90Vwith reactive gases such as oxygen and nitrogen; and from aboutVd� 80–100V for aclosed electron drift with noble gases and up to about 360–370V for both ion sources.It can only exist and be maintained due to a continuous development of chargedparticles provided by a source of electrons.

With xenon as theworking gas, discharge can be ignited by about 15–20V lower forboth ion sources. The discharge voltage ignition values given above are for approx-imate equality of discharge and emission currents. For emission currents thatsubstantially exceed the discharge current (discussed in Chapter 4), the ignitionvoltage can be 20–30V lower. CDIS have, as a rule, higher ignition voltages than end-Hall ion sources. Various ignition discharge voltages can be explained by the fact thataCDISmainly has a radialmagneticfield component in thewhole discharge channel,and end-Hall has a radial magnetic field component only at the exit from an ionsource. So, for electrons generated outside the ion source discharge channel, it ismore difficult to go through a higher radialmagneticfield component in a closed driftsource than in an end-Hall source.

0

1

2

3

4

5

6

7

8

9

10

500450400350300250200150100500

Discharge voltage Vd, V

Dis

char

ge c

urre

nt, I

d, A

; Ion

bea

m c

urre

nt Ii

, A

Id = Iem = 5 A

I at I = Ii d em = 5 A

1

2

Concentrateddischarge

Distributeddischarge

Nonself-sustaineddischarge

Self-sustaineddischarge

Figure 1.21 V–A characteristics, regimes, andmodes for end-Hall ion source with discharge Id andion beam current Ii as functions of discharge voltage Vd for Id¼ Iem¼ 5 A; working gas argon.


As noted above, a high current discharge in ion sources with a discharge voltageover Vd� 370–380V presents itself as a self-sustained discharge, when it is notnecessary to supply electrons from a cathode neutralizer for neutralization of ions.After discharge is initiated, a high voltage discharge produces sparks, creatingelectrons in the discharge channel and outside of an ion source in the vacuumchamber walls.

Also, discharge at low discharge voltages and up to about Vd¼ 200–220V (argon)presents itself as a modification that is a distributed discharge. Discharge at higherdischarge voltages (above about 220V) presents itself as a modification called aconcentrated discharge. These modifications received such names because they areobserved from outside a vacuum chamber as distributed and concentrated forms ofdischarge, meaning that a distributed discharge is really uniformly distributed over adischarge channel area, and a concentrated discharge can be seen in the form ofplurality of pinched plasma flows, and at high currents of 10 A and above as onepinched discharge surrounded by a glow.

Both kinds of intensive discharge, nonself-sustained (in a distributed mode) andself-sustained (in a concentrated mode), are significantly different in their physicalprocesses. The processes taking place in a distributed discharge are more complexand have been less investigated. In particular, for propagation of electron currentfrom the cathode to the anode, it is necessary to have excessive plasma conductivity,which under certain conditions can be caused by the development of oscillations ofcurrent and voltage. At the same time, the total relative amplitude of ion beamcurrent oscillations in a distributedmode is substantially lower than in a concentrateddischarge.

In one of the publications about closed drift anode layer type ion sources-thrusters [23], experimental results with discharge are presented where theworking gas was xenon. In the anode layer, an ion source thruster havingdimensions of exit discharge channel diameter of 80mm, the discharge distrib-uted mode was at discharge voltages of less than 250 V. It was noted that at adistributed form of discharge, the ion flow parameters at the source exit are moreuniform than at a concentrated modification. Also, an ion beam focusing qualityon a distributed mode is better than in a concentrated modification. The exactvalues of discharge voltage for transition from one form into another depend on:(1) dimensions and geometry of the discharge channel, (2) discharge current,(3) working gas mass flow, and (4) magnetic field components and their values in adischarge channel.

BesidesV–Acharacteristics (Figure 1.21),which are not easy to properly investigatefor regular ion source users, there is another important characteristic: the dischargevoltage as a function of the working gas mass flow Vd¼ f( _ma) at constant dischargecurrents, Id¼ 1, 2, 3, 4, 5. . .10 A. Typical characteristics of Vd¼ f( _ma) and Id¼ 1, 3, 5A for oxygen, argon, and krypton for new end-Hall ion sources with a multichamberanode [21] are given in Figure 1.22.

A well-tuned ion source always shows smooth curves for Vd¼ f( _ma). Usually,such curves begin showing erratic behavior at low and high discharge voltages,when discharge experiences various oscillations. In addition, many producers of


ion sources with a narrow range of operating discharge voltages could not finda proper optimum magnetic field in a discharge channel. Also, tested curves ofVd¼ f( _ma) become quite narrow. For example, one can see (Figure 1.22) that foroxygen (nitrogen behaves in similar way), the discharge voltage at its low value doesnot go lower than about Vd¼ 80–90 V. However, by regulation of a permanentmagnet�s magnetic field, it is possible to have oxygen with a discharge voltage ofVd¼ 40–50 V.

Figure 1.22 presents experimental data for a recently developed new end-Hallion source [21] for the discharge voltage as a function of aworking gasmass flowVd¼f( _ma) for constant discharge currents Id¼ 1, 3, 5 A for oxygen, argon, and krypton. Asone can see, at high discharge voltages a working gasmass flow is quite low; for mostgases it is under 5–10 sccm for low discharge currents and, especially, for krypton. Aworking gas mass flow is influenced by the ionization potential (low first ionizationpotential gases have higher ionization cross section) and atomic ormolecular weight.Also, the vacuum chamber size, its pumping means, and the dimensions of an ionsource opening diameter have an influence on the applied working gasmass flow. Ingeneral, the larger a vacuum chamber, the bigger the ion source dimensions, thehigher is the mass flow of a working gas required.

As discussed at the beginning of this book, the most important characteristicvalues of any industrial ion source are: an ion beam current value Ii, and a mean ionbeam energy Ei. Both values are not given on power supplies and are not easyto measure; there are special probes for this purpose(discussed in Chapter 9). The

Figure 1.22 End-Hall ion source [21] discharge voltage as function of a working gas mass flowVd¼ f( _ma) at constant discharge currents Id¼ 1, 3, 5 A for oxygen, argon and krypton.


results of an ion beam current as a function of discharge voltage Ii¼ f (Vd) at constantdischarge currents Id¼ 1, 3, 5A for oxygen, argon, and krypton for a newend-Hall ionsource with a multichamber anode are presented in Figure 1.23.

Comparing this figure�s curves with Figure 1.21, there are definite similarities inthe behavior of the curves for an ion beam current for all tested gases. Allexperimental curves are taken with an external cathode in the form of HF, withdischarge current and neutralization currents approximately equal to each other,or Id� Iem. All curves show a typical nonself-sustained discharge with a maximumion beam current in the range of discharge voltages from about Vd¼ 100–150Vat alldischarge currents and for all working gases.

The above discussions of various V–Acharacteristics, regimes, andmodes for end-Hall ion sources are due to the fact that formost of the time, end-Hall ion sources areutilized in the range of discharge voltages from about Vd¼ 50–80V (if possible) andup to about 150–175V. However, in practice, Vd¼ 100V is the most probableexperimental value with Id¼ 1–5 A.

It is necessary to note that the behavior of curves, such as the initial dischargevoltage (discharge ignition), an ion beam current value, and the ranges of variousdischarge types and modes depend not only on the emission current value, but alsoon the following factors:

1) Mass flow of working gas applied into a discharge channel and pressure in thevacuum chamber: the higher the mass flow, the lower the discharge voltageignition.

Figure 1.23 End-Hall ion source [21], ion beam current as function of discharge voltage Ii¼ f(Vd) atconstant discharge currents Id¼ 1, 3, 5 A for oxygen, argon and krypton.


2) Dimensions and shape of an ion source discharge channel.3) Magnetic field value and ion source magnetic circuit configuration.4) Gas distributing system; how the working gas is applied into the anode region;

how the working gas is distributed in the discharge channel, whether it comesfrom an area under the anode (could be applied first into a so-called buffer area)and well distributed there, applied through small jets from gas-supply holes, orfrom the anode itself.

5) Emission current value supplied by an HF, HC, or other means; how emissionprovides a flow of electrons into a discharge channel; how the electron sourcesare placed and at what distance from the exit flange of the ion source.

6) Type of working gas: low or high atomic mass, ionization potential.

1.5Operating Parameters Characterizing Ion Source

The cylindrical Hall-current ion sources can operate with many different workinggases. However, a majority of work in industrial utilization of ion sources is withgases such as oxygen, nitrogen, argon, other noble gases (xenon, krypton), methane,and hydrogen. The most important operation characterizing parameters of cylin-drical Hall-current ion sources are:

1) Range of Discharge Voltages, Vd: Hall-current ion sources can usually operatefrom about Vd¼ 50–80V to about Vd¼ 1000V. The range of discharge voltagestranslates into an ionbeamenergy (ions born in electric discharge are acceleratedby applied electric potential between the anode and the cathode). Most closeddrift and end-Hall ion sources have a very broad ion beam energy distributionwith a mean ion energy Ei¼ (0.6–0.7) eVd, though recently developed new ionsources are capable of having a narrow ion beamenergy distributionwith ameanenergy Ei¼ (0.8–0.9) eVd. This is for properly neutralized ion sources. In thesecases, when an ion beam is not neutralized by an external source of electrons, orunderneutralized with the emission current lower than the discharge current, amean ion energy Ei¼ (0.1–0.5) eVd. In academic studies of Hall-currention sources [1], this feature of a discharge voltage conversion into an ionbeam mean energy is characterized by the coefficient of the ion beam energytransformation, or the ratio of a mean ion beam energy to the applied electricpotential to anode times the electron charge:

k1 ¼ kE ¼ Ei=eVd ð1:1ÞMost ion source users do not pay much attention to this coefficient; however,

we are going to show later that this value is important in many thin filmdeposition tasks.

2) Range of Discharge Currents, Id: Hall-current ion sources can usually operatefrom about Id¼ 1–2 A to Id¼ 10–15 A. In principle, it is possible to design ionsources with substantially higher discharge currents of up to Id¼ 50–100 A.


However, such high discharge currents would need a large-diameter dischargechannel with high working gasmass flows that must be pumped from a vacuumchamber and big power supplies. This requires high-production vacuumpumps, a lot of energy, and big financial expenditures. Also, such high dischargecurrentsmay not be necessary for most designed technical tasks. Only in specialoccasions such discharge currents can be justified.

The range of discharge currents translates into an ion beam current, or howefficient the design for an ion source is for a discharge current transformationinto an ion beam current. This feature is usually characterized by the coefficient ofthe discharge current transformation into the ion current:

k2 ¼ ki ¼ Ii=Id ¼ _mae=ðMIdÞ ð1:2Þwhere _ma is a working gasmass flow, e is the electron charge, andM is a workinggas atomic mass. The coefficient ki for ALIS and MLIS is 0.8–0.9 in optimumregimes with correctly used magnetic field and with the external source ofelectrons for ion beamneutralization. For end-Hall ion sources, this coefficient isusually 0.2–0.25.

3) Relative Monoenergeticity of an Ion Source�s Ion Beam Energy: This feature ischaracterizedby the coefficient determining the ratioof a certain rangeof energiesaround the mean ion beam energy (for example, a 90% from the total ionbeam energy distribution) to the electron charge times the discharge voltage, or:

k3 ¼ kDE ¼ Mhv2i i=ð2 eVdÞ ð1:3Þ4) Ion Beam Divergence: At the ion source exit, which is determined by a certain

percentage (70–80%) of a total ion beam current density ji passing from an ionsource axis through a conical surface with an opening half-angle a of 10–15�

(ALIS with proper ion beam neutralization), 20� (MLIS with proper ion beamneutralization), and 40–60� (end-Hall ion source with proper ion beam neu-tralization). The coefficient determining impact of an ion beam flow divergence can bedetermined as:

k4 ¼ ka ¼ hvizi2=hv2i i ð1:4Þwhere viz and vi are ion particles velocity in the z-direction, and total ion flow.

5) The Coefficient of the Working Material Utilization:

k5 ¼ k _ma ¼ _mi= _ma ð1:5ÞThis coefficient k _ma

together with ki coefficient shows how efficient theparticular ion source is in transformation of a working material into an ionbeam flow.

6) In some cases, it is necessary to take into account the coefficient determining anumber of doubly ionized particles, or a current of theworking gas and their ratio toa number of singly ionized particles, or a current with:

k6 ¼ kzþþ ¼ Ii;zþþ =Ii;zþ ð1:6Þ

1.5 Operating Parameters Characterizing Ion Source j25

This coefficient can be from 10�4 for low ion beammean energies, up to 10�1

at moderate energies of about 300 eV, and up to 0.5 and more at higher energiesof above 500–800 eV. Coefficient kzþþ also depends not only on ion beamenergies, but on a working gas first ionization potential and a gas pressure. Insome cases, even a small coefficient kzþþ can have a great impact on certain thinfilm processes, because the doubly ionized particles possess double ion energythat can cause substantial sputtering of materials. This coefficient, along withsome specific operations of ion sources, will be discussed in another chapter.

7) Coefficient determining the ratio of ionized particles flying into the direction of an ionbeam exit Ii,direct and a number of ions, or a current flowing into the opposite directionIi,reverse, into a reflector, the place where a gas distributor is located:

k7 ¼ krev ¼ Ii;reverse=Ii;direct ð1:7ÞThis coefficient is especially important for end-Hall ion sources in which a

substantial flow of ions is directed into a gas distributor-reflector in the oppositedirection of the exit plane. This flow of ions falls on a reflector�s surface, sputters it,reflects back to the exit plane, andmakes an ion beam contaminated with a reflector�smaterial. In some cases, the coefficient krev can be from 10�4 to 10�2, which is quite alarge number. This reverse flow produces substantial damage to a gas distributingsystem-reflector, and the reflector must be substituted for a new one within 15–20 hof operation at Id¼ 5 A and Vd¼ 100–150V.

Appendix 1.A: Web Addresseshttp://www.orc.ru/�platar/P6E.html.http://www.mirea.ru/science/priority/plazm.html.http://www.veeco.com/linear-anode-layer-ion-sources/index.aspx.http://generalplasma.com/products/ion-sources/ppals-ion-source.http://glass-coatings.narod.ru/ionsource_ru.htm.

References

1 Belan, N.V., Kim, V.P., Oransky, A.I., andTikhonov, V.B. (1989) Stationary PlasmaThrusters. Kharkov Aviation Institute (inRussian).

2 Zhurin, V.V., Kaufman, H.R., andRobinson, R.S. (1999) Physics of closeddrift thrusters. Plasma Sources Sci. T., 8,R1–R20.

3 Kimock, F., Finke, S., Brown, D., andThear, E. (1999) The Evolution of Ion-Beam Diamond Like-CarbonTechnology into Data Storage: SpacePropulsion, Sunglasses, Slides, andNewDisks, DataTech Magazine, 2nd edn, pp.69–77.

4 Knapp, B. and Finke, S. (2003) Direct ionbeam chemical vapor deposition of SiO2-like materials using a closed-drift ionsource. Society of Vacuum Coaters, 46th

Annual Technical ConferenceProceedings.

5 Grishin, S.D. and Leskov, L.V. (1989)Electric Rocket Thrusters of SpaceApparatuses,Mashinostroenie,Moscow (inRussian).

6 Titishov, B.N. and Lebedev, S.V.(2–5October 1973) Stationary plasmasource of low-energy ions. IIAll-Union Conference on Plasma


Accelerators, Minsk, pp. 101–102 (inRussian).

7 Kaufman,H.R. andRobinson, R.S.(Aug 291989) End-Hall Ion Source, US patent4,862,032.

8 Choi, M. and Zhurin, V.V. (April 17–212010) End-Hall ion sources with reducedheat to a magnet. 53rd Annual SVCTechnical Conference & Exhibit.

9 Babaiants,G.I.,Zhupanov,V.G.,andKlyuev,E.V. (2002) Calculation and Fabrication ofLaserWindows withHigh RadiationStability. 9th Russian Conference �VacuumScience and Technology�, Moscow.

10 Zhurin, V.V. (Dec 25 2007) Hall-CurrentIon Source for Ion beams of Low andHighEnergy for Technological Applications, USPatent 7,312,579.

11 Svirin, V.T. and Stogny, A.I. (1996), N 5Formation of equilibrium density beam ina hall ion source with opened end. Russ. J.Pribory (Instrum.) and Exp. Techniques (5),103.

12 Sainty, W. (November 11 2003) Ion Source,US Patent 6,645,301.

13 Burtner, D.M., Townsend, S.A., Siegfried,D.E., and Zhurin, V.V. (March 11 2008)Fluid-Cooled Ion Source, US Patent No.7,342,236.

14 Zhurin, V.V. (November 2009) IndustrialGridless Broad Beam Ion Sources and theNeed for Their Standardization. Part 4B.Hall-Current Ion Sources, Problems andSolutions. Standardization of Ion Sources,Vacuum Technology & Coating, pp. 40–49.

15 Klyuev, V. (October 2009) PrivateCommunication.

16 Kaufman,H.R.,Kahn, J.R., Robinson,R.S.,and Zhurin, V.V. (June 15 2004) Hall-Current Ion Source, US Patent 6,750,600.

17 Morozov, A.I. (1973) On equilibrium andstability of flows in accelerators with closedelectron drift and extended accelerationzone, in Plasma Accelerators, collection ofpapers from the 1st All-Union Conferenceon Plasma Accelerators,Maschinostroenie, Moscow, p. 85 (inRussian).

18 Raitses, Y. and Fisch, N.(September 102002) Cylindrical Geometry Hall Thruster,US Patent No. 6,448,721.

19 Zhurin, V.V. (October 2006) High-EfficientIon Source with Improved Magnetic Field,US Patent No. 7,116,054.

20 Tang, D., Wang, L., Pu, S., Cheng,C. and Chu, P.K. (2007)Characteristics of end-Hall ionsource with magnetron hollow cathodedischarge. Nucl. Instrum. Methods B., 257,796–800.

21 Klyuev, E.V. andZhurin,V.V. (July 29, 2010)Hall-Current Ion Source with ImprovedIon Beam Energy Distribution, PatentApplication 12/804,763.

22 Liapin, E.A. and Semenkin, A.V. (1990)Modern state of investigations ofaccelerators with anode layer, in IonInjectors and Plasma Accelerators ( A.I.Morozov et al.) Publishing House�Energoatomizdat�, Moscow, p 20–33(in Russian).

23 Barannikov, A.L., Grishin, S.D.,Marakhtanov, M.K., and Pil�nikov, A.V.(26–28 September 1989)Low-voltage plasma accelerator withanode layer. VII All-UnionConference on Plasma Accelerators andIon Injectors, Kharkov, pp. 208–209 (inRussian).

References j27

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